Early access · courses are being reviewed by field engineers
Service EngineerAcademy
My learningSign inRU
Academy / Field fault notes / Puritan Bennett 840
Puritan Bennett · 840

Puritan Bennett 840: power-up self-test fails after long storage

What happened

After a long period of idling, the ventilator failed its power-up self-test, an old battery fault stayed latched in the logs, and an O2 sensor error appeared even though a fresh sensor was fitted.

What was checked

Cause

The engineers found that after the long storage the batteries were dead, and their condition dragged the power-up self-test down, so the test failed and the battery error stayed latched. The O2 sensor complaint cleared once the test passed, so it looked like a collateral symptom of the failed test rather than a sensor fault.

What was done

With the ventilator switched off and unplugged, fully disconnect the battery block cable, then power the unit on and run the power-up self-test. As reported in this case, the test passed and the errors cleared with the dead battery block left disconnected — the batteries themselves still needed replacement before the unit could rely on battery backup.

Safety

Power the ventilator off and unplug it from mains before disconnecting the battery cable — batteries store energy and can short or leak after long storage; a unit with the battery block disconnected has no backup power and must not return to clinical use until the batteries are replaced, the full self-test passes and electrical safety is verified.

Lesson: A dead battery can hold down the whole power-up self-test and pull in unrelated-looking errors, so after long storage check the batteries first before chasing individual sensor faults.

Covered in the course: Ventilator Service — Level 2: Fault-Finding →

Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.

← All notes